[PATCH v2] pid: Fix error return value in some cases

[PATCH v2] pid: Fix error return value in some cases

[minyard]

From: Corey Minyard <cminyard@mvista.com>

Recent changes to alloc_pid() allow the pid number to be specified on
the command line.  If set_tid_size is set, then the code scanning the
levels will hard-set retval to -EPERM, overriding it's previous -ENOMEM
value.

After the code scanning the levels, there are error returns that do not
set retval, assuming it is still set to -ENOMEM.

So set retval back to -ENOMEM after scanning the levels.

Fixes: 49cb2fc42ce4 "fork: extend clone3() to support setting a PID"
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Cc: <stable@vger.kernel.org> # 5.5
Cc: Adrian Reber <areber@redhat.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Andrei Vagin <avagin@gmail.com>
---

Changes from v1:
  Just set retval to -ENOMEM before the gotos that would use it.

I do think that the second instance:

        if (!(ns->pid_allocated & PIDNS_ADDING))
                goto out_unlock;

is returning the wrong error value, but that's probably not a big
deal, and if it was fixed would probably need to be a separate change.

In the first instance, the error return values are almost all -ENOMEM,
anyway.

 kernel/pid.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/pid.c b/kernel/pid.c
index 0f4ecb57214c..19645b25b77c 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -247,6 +247,8 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
 		tmp = tmp->parent;
 	}
 
+	retval = -ENOMEM;
+
 	if (unlikely(is_child_reaper(pid))) {
 		if (pid_ns_prepare_proc(ns))
 			goto out_free;
-- 
2.17.1

Re: [PATCH v2] pid: Fix error return value in some cases

[Christian Brauner]

On Fri, Mar 06, 2020 at 11:23:14AM -0600, minyard@acm.org wrote:
> From: Corey Minyard <cminyard@mvista.com>
> 
> Recent changes to alloc_pid() allow the pid number to be specified on
> the command line.  If set_tid_size is set, then the code scanning the
> levels will hard-set retval to -EPERM, overriding it's previous -ENOMEM
> value.
> 
> After the code scanning the levels, there are error returns that do not
> set retval, assuming it is still set to -ENOMEM.
> 
> So set retval back to -ENOMEM after scanning the levels.
> 
> Fixes: 49cb2fc42ce4 "fork: extend clone3() to support setting a PID"
> Signed-off-by: Corey Minyard <cminyard@mvista.com>
> Cc: <stable@vger.kernel.org> # 5.5
> Cc: Adrian Reber <areber@redhat.com>
> Cc: Christian Brauner <christian.brauner@ubuntu.com>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Dmitry Safonov <0x7f454c46@gmail.com>
> Cc: Andrei Vagin <avagin@gmail.com>

Thanks! I've pulled the patch now and applied.

I think that restores the old behavior. If you don't mind, I'll add a
comment on top of it saying something like:
"ENOMEM is not the most obvious choice but it's the what we've been
 exposing to userspace for a long time and it's also documented
 behavior. So we can't easily change it to something more sensible."

Acked-by: Christian Brauner <christian.brauner@ubuntu.com>

Re: [PATCH v2] pid: Fix error return value in some cases

[Corey Minyard]

On Sat, Mar 07, 2020 at 12:00:07PM +0100, Christian Brauner wrote:
> On Fri, Mar 06, 2020 at 11:23:14AM -0600, minyard@acm.org wrote:
> > From: Corey Minyard <cminyard@mvista.com>
> > 
> > Recent changes to alloc_pid() allow the pid number to be specified on
> > the command line.  If set_tid_size is set, then the code scanning the
> > levels will hard-set retval to -EPERM, overriding it's previous -ENOMEM
> > value.
> > 
> > After the code scanning the levels, there are error returns that do not
> > set retval, assuming it is still set to -ENOMEM.
> > 
> > So set retval back to -ENOMEM after scanning the levels.
> > 
> > Fixes: 49cb2fc42ce4 "fork: extend clone3() to support setting a PID"
> > Signed-off-by: Corey Minyard <cminyard@mvista.com>
> > Cc: <stable@vger.kernel.org> # 5.5
> > Cc: Adrian Reber <areber@redhat.com>
> > Cc: Christian Brauner <christian.brauner@ubuntu.com>
> > Cc: Oleg Nesterov <oleg@redhat.com>
> > Cc: Dmitry Safonov <0x7f454c46@gmail.com>
> > Cc: Andrei Vagin <avagin@gmail.com>
> 
> Thanks! I've pulled the patch now and applied.
> 
> I think that restores the old behavior. If you don't mind, I'll add a
> comment on top of it saying something like:
> "ENOMEM is not the most obvious choice but it's the what we've been
>  exposing to userspace for a long time and it's also documented
>  behavior. So we can't easily change it to something more sensible."

That's great.  I was just looking through the code for another reason
and noticed the issue.  Every little thing counts for quality.

-corey

> 
> Acked-by: Christian Brauner <christian.brauner@ubuntu.com>

Re: [PATCH v2] pid: Fix error return value in some cases

[Christian Brauner]

On Sat, Mar 07, 2020 at 07:11:36AM -0600, Corey Minyard wrote:
> On Sat, Mar 07, 2020 at 12:00:07PM +0100, Christian Brauner wrote:
> > On Fri, Mar 06, 2020 at 11:23:14AM -0600, minyard@acm.org wrote:
> > > From: Corey Minyard <cminyard@mvista.com>
> > > 
> > > Recent changes to alloc_pid() allow the pid number to be specified on
> > > the command line.  If set_tid_size is set, then the code scanning the
> > > levels will hard-set retval to -EPERM, overriding it's previous -ENOMEM
> > > value.
> > > 
> > > After the code scanning the levels, there are error returns that do not
> > > set retval, assuming it is still set to -ENOMEM.
> > > 
> > > So set retval back to -ENOMEM after scanning the levels.
> > > 
> > > Fixes: 49cb2fc42ce4 "fork: extend clone3() to support setting a PID"
> > > Signed-off-by: Corey Minyard <cminyard@mvista.com>
> > > Cc: <stable@vger.kernel.org> # 5.5
> > > Cc: Adrian Reber <areber@redhat.com>
> > > Cc: Christian Brauner <christian.brauner@ubuntu.com>
> > > Cc: Oleg Nesterov <oleg@redhat.com>
> > > Cc: Dmitry Safonov <0x7f454c46@gmail.com>
> > > Cc: Andrei Vagin <avagin@gmail.com>
> > 
> > Thanks! I've pulled the patch now and applied.

Applied as:
https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/commit/?h=fixes&id=b26ebfe12f34f372cf041c6f801fa49c3fb382c5

Should show up in -next around Monday and I'll target it for rc6. Should
then be backported to v5.5 rather soon!

Thanks!